1. Field of the Invention
The present invention relates to a resin tablet used for plastic encapsulation of semiconductor devices and a method of manufacturing a plastic package such as a resin encapsulated semiconductor device using such resin tablet.
In the manufacture of resin encapsulated semiconductor devices, that is, plastic package semiconductor devices, resin encapsulation is effected by transfer molding techniques using a resin tablet obtained by compressing a powdered resin for molding as the supply material.
In transfer molding, since a molding die pot is used as the molding material supply port and the molding resin is transferred therefrom to the molding die resin path with the pressure in the plunger engaged with the pot, the supply material is tablet-shaped so that it fits to supply the pot.
In conventional molding, resin tablets, which are formed only by compressing the powder of thermosetting resin for molding with the resin exposed, are used as the supply material.
Therefore, when this resin tablet touches other objects, the resin powder easily separates and leaps away from the surface of tablet. Accordingly, when this resin tablet used, the powder scatters and is adheres to every corner during delivery to the molding die pot. This powder soils workers' hands during manual processing. In addition, the powder also causes electric contacts of molding die to fail, and leads to errorneous recognition of photosensor. The powder also tends to adhere to a new resin tablet, after curing, and enters the resin to be transferred during the molding process, resulting in a problem that the molding quality is deteriorated.
For this reason, if it is attempted to take a measure for the process of transfer molding, it is extremely difficult so long as the conventional resin tablet is used.
In addition, the resin tablet is formed in the specified resin condition mixing the base resin, hardening agent, filler and other additives and it provides a problem that if it is taken out from the encapsulation package and is left for a while, quality declines due to absorbed humidity, which leads to a deterioration of molding quality of encapsulating package. Therefore, the resin tablet which has been left for the predetermined period after the hermetically sealed package is opened is no longer used and it is desirable that the resin tablet can further be used even after the capsule is opened and the resin is left for a long period (for instance, half day to several days) under ambient conditions.